The present invention relates to mass spectrometers.
In mass spectrometers used for proteome analysis, orthogonal time-of-flight mass spectrometers (hereinafter, called orthogonal-TOF mass spectrometers), that is, time-of-flight mass spectrometers in which the ion introduction direction into the TOF part is orthogonal to the ion acceleration direction in the TOF part are widely used. How analysis of these has been conducted will be described below.
There is a report about the orthogonal-TOF mass spectrometer (for instance, see A. N. Krutchinsky et al.: Proceedings of the 43rd ASMS Conference on Mass Spectrometry and Allied Topics, 1995, p. 126 (Conventional Method 1)). Multipole rods are provided in a vacuum chamber evacuated to about 10 Pa directly before the TOF part. In a region surrounded by the multipole rods, ions collided with a gas lose kinetic energy to be focused near the center axis. The ions which have passed through the multipole rods to be introduced into the TOF part are accelerated in the direction orthogonal to the ion introduction direction. The initial distribution of position and the initial distribution of kinetic energy in the acceleration direction are reduced to increase the mass resolution in the TOF part.
There is a report in which this method is improved to increase the duty cycle of the orthogonal-TOF mass spectrometer (for instance, see U.S. Pat. No. 5,689,111 (Conventional Method 2)). A potential gradient is provided between multipole rods in the previous stage of the TOF part and an end lens disposed on the exit side to trap ions in a multipole chamber. The potential gradient is inverted in pulse to eject the ions trapped in the multipole chamber to the TOF part. An accelerating voltage is applied in synchronization with the timing at which the ejected ions reach the accelerator of the TOF. The duty cycle in the specific mass range can be increased to almost 100%.
There is a report in which the duty cycle in the orthogonal-TOF mass spectrometer in Qq-TOF combining a quadrupole mass filter with the orthogonal-TOF mass spectrometer (for instance, see U.S. Pat. No. 6,507,019 (Conventional Method 3)). In the Qq-TOF, a collision cell is provided between a quadrupole mass filter selecting precursor ions and the TOF part. The collision cell is a vacuum chamber evacuated to about 10 Pa in which multipole rods are arranged. The ions selected by the quadrupole mass filter are dissociated by collision with a gas in the region surrounded by the multipole rods, and then lose kinetic energy by collision with the gas to be focused near the center axis. A potential gradient is provided between the multipole rods in the previous stage of the TOF part and an end lens disposed on the exit side to trap the ions in the multipole chamber. The potential gradient is inverted in pulse to eject the ions trapped in the multipole chamber to the TOF part. An accelerating voltage is applied in synchronization with the timing at which the ejected ions reach the accelerator of the TOF. The duty cycle in the specific mass range can be increased to almost 100%.
In a method of ejecting ions in the specific mass range from a multipole linear trap in mass spectrometers used for proteome analysis, how analysis of these has been conducted will be described below.
There is a report about a method of ejecting ions in the specific mass range from a multipole linear trap (for instance, see U.S. Pat. No. 5,783,824 (Conventional Method 4)). In this method, vane electrodes are inserted between multipole rods to apply a DC voltage for forming an electrostatic harmonic potential in an axial direction. A supplemental AC voltage is applied between the vane electrodes divided into two or more in the axial direction to resonate ions in the axial direction. The resonant ions are beyond the electrostatic harmonic potential formed in the axial direction to be ejected in the axial direction. The resonant frequency is different depending on mass. The ions can be mass selectively ejected in the axial direction.
There is a report about a method of ejecting ions in the specific mass range from a quadrupole linear trap (for instance, see U.S. Pat. No. 6,177,668 (Conventional Method 5)). A DC potential is applied between an end lens and quadrupole rods to accumulate ions in a linear trap. A supplemental AC voltage is applied between the quadrupole rods or between the quadrupole rods and the end lens to come into resonance with a quadrupole or octapole component in the diameter direction which is originally formed in the quadrupole linear trap. Kinetic energy provided in the diameter direction is converted in an axial direction. The ions are beyond a DC potential formed between the end lens and the quadrupole rods to be ejected in the axial direction. The resonant frequency is different depending on mass. The ions can be mass selectively ejected in the axial direction.
There is a report in which the duty cycle in the specific mass range in the MS/MS analysis mode by combining ejection in the specific mass range from amultipole linear trap with the orthogonal-TOF mass spectrometer (for instance, see U.S. Pat. No. 6,504,148 (Conventional Method 6)). A mass analyzer, collision cell, and mass spectroscopic means are provided. The method of mass selectively ejecting ions disclosed in Conventional Method 5 is used for at least one of the mass analyzer and ejection from the collision cell. The duty cycle in the specific mass range can be increased.